Might have to rethink the grounding point for the strap too ... the PT bolts are kept a bit loose and have insulators to reduce mechanical noise. Wouldn't be too difficult to add a hard mount between the two transformer screw holes. That would be hidden by the PT up top. Hmmmmmmmm ...

Then again, noise isn't an issue. I can hear a very slight hum out of the speakers on idle, but then again, they're cranked up pretty good as a rule. I get more mechanical noise from the transformers and the fish tank in the other room, but I'll put this on my ponder list ... I keep that right next to my to do list ... which is somewhere or other.

(Note to self, add to my to do list ... find a better place to keep my to do list.)

corndog71 wrote:The quad-cap always seemed like a deeply flawed design to me which is why I didn't include it in my amp.

The quad cap is not deeply flawed. What happens is that ANY ELECTROLYTIC cap has a finite life span. It is like the battery in your car. In time, because of chemical changes inside the battery, it will eventually go bad.

In the original Dynaco amps that one quad cap stored all the high voltage DC for the entire amp - SO - 40 to 60 years later when someone finds an old Dynaco amp what is the one thing that might be bad > the quad cap - so people assume that ALL QUAD CAPS are bad or are a bad design. The quad cap is four electrolytic caps in one structure - SO - what do people do > they replace the quad cap with a "cap board" and think that their trouble are over because the cap board is "much better." The cap board is NOT much better. What you have on the cap board are EIGHT electrolytic caps that replace the FOUR sections of the quad cap. Those eight caps will ALSO eventually go bad because of chemical changes withing the cap. This is one of the most oft repeated flawed interpretations of Dynaco tube amps. The MOST repeated flawed Dynaco tube amp interpretation is about those "desirable cloth lead Dynaco output transformers" being the "holy grail" of output transformers. This is bull$h!t. Those original Dynaco output transformers have been cloned quite easily simply by unwinding the transformer and counting the turns per winding and then programming a transformer winding machine to duplicate the transformer. Read the link below from our forum from about 5 years ago about the windings on the Dynaco A-470 output transformer.

Tell it like it is Bob....hehe....thanksI love this old tube steff.....but lot of myths out there...but hay for 50 year old Mk3s I gave $100. for the pr with the sock GE 6550s..s long as I keep the Varic at 110ac....an..sound dame good up agents the jadis defy7....this youtube guy post a lot of tube info....fun facts may help us...Good fun....

corndog71 wrote:The quad-cap always seemed like a deeply flawed design to me which is why I didn't include it in my amp.

The quad cap is not deeply flawed. What happens is that ANY ELECTROLYTIC cap has a finite life span. It is like the battery in your car. In time, because of chemical changes inside the battery, it will eventually go bad.

In the original Dynaco amps that one quad cap stored all the high voltage DC for the entire amp - SO - 40 to 60 years later when someone finds an old Dynaco amp what is the one thing that might be bad > the quad cap - so people assume that ALL QUAD CAPS are bad or are a bad design. The quad cap is four electrolytic caps in one structure - SO - what do people do > they replace the quad cap with a "cap board" and think that their trouble are over because the cap board is "much better." The cap board is NOT much better. What you have on the cap board are EIGHT electrolytic caps that replace the FOUR sections of the quad cap. Those eight caps will ALSO eventually go bad because of chemical changes withing the cap. This is one of the most oft repeated flawed interpretations of Dynaco tube amps. The MOST repeated flawed Dynaco tube amp interpretation is about those "desirable cloth lead Dynaco output transformers" being the "holy grail" of output transformers. This is bull$h!t. Those original Dynaco output transformers have been cloned quite easily simply by unwinding the transformer and counting the turns per winding and the programming a transformer winding machine to duplicate the transformer. Read the link below from our forum from about 5 years ago about the windings on the Dynaco A-470 output transformer.

I agree with you in most points Bob, but there is nothing wrong with using a cap board instead of the can cap. Both will work just fine for many years, and yes, of course like most components, they will eventually 'wear out' and fail. As long as good quality caps are used, be it the can or cap board, and importantly that the caps are not overstressed by operating too close to their rated voltages, all should be good.And yes, I agree, replacing the can cap with a cap board is not a magic fix, it comes down to preference.

I mostly agree with MontanaWay on this one. All electrolytic caps do have a limited lifespan.....discrete caps and quad caps. So there is nothing conceptually wrong with a new quad cap, the problem is today's higher AC wall voltage. Most places in the US have wall voltage between 122 volts to as much as 130 volts (I have 126 volts at my house). Roughly 10% higher than wall voltage in the 60's, this can translate to an additional 40-60 volts DC hitting the first stage of the quad cap. This can easily exceed the voltage rating of a new replacement quad cap (ask me how I know!) and you quickly have a $40 door stop! This is the problem with current-manufacture quad caps......they don't have sufficient voltage rating. This why I've stopped using quad caps in both hifi and guitar amps. The replacement cap boards use 8 caps, stacked in pairs in totem-pole fashion with balancing resistors. The stacked caps, usually 350 volt each, then have a combined rating of 700 volts, easily exceeding the output from the rectifier. So, no blown filter caps! This is why the cap board IS MUCH better than the quad cap and really not a preference (unless you have uncommonly low wall voltage or like replacing quad caps on a regular basis). The other problem with quad caps is that that all four sections utilize a common ground. This can create hum problems with integrated amps and guitar amps due to the inability to separately ground the filter caps with their respective stages. This can easily be done with a cap board. If manufacturers would build can caps with a higher voltage rating, then drop-in replacement would be a cinch in our old Dynaco gear.

I was in the Audio Biz in the 80-90s...Today buy an sale from time to time....fisher,hhscott,Eico,HeathAn Dynacos....an do some retubeing for fokes.....an ALL sale comes with a Varic....Yes the AC is way to high for any old Tube amps....An I have found the sound is much better with a B+ of 480-90 on most an as for the old tube pramps....Droping there B+ is a real + sound wise as the heaters also drop....It like a tone shaping...hehe....most cant believe what a Varic Can do to give better tube tone....Have fun with tubes....life is short

66tele wrote:The stacked caps, usually 350 volt each, then have a combined rating of 700 volts, easily exceeding the output from the rectifier. So, no blown filter caps!

This is not correct at least of the Triode Electronics (SDS) ST-70 cap board. The first section of the this board is 800 volt rated using two 400 volt caps (C1 and C2) in series. The next three sections (C3 - C8) use 250 volt caps in series, and as such, they are only 500 volt rated. All the VTA amps use 550 volt rated quad caps that are 600 volt surge rated. Check the parts list on the Triode Electronics cap board at the link below ...

Agree with you, Bob, that the quad caps are not "deeply flawed." They have been successfully in use for decades and are still viable.

But, with regard to the Triode USA cap board for the Stereo 70, yes, sections two through four are rated for 500 working volts DC. But, the second section should actually see about 415 volts DC with the third and fourth sections less than that.

If someone’s wall voltage were so high that these sections rose to 500 VDC, then the amp might run into other problems as well (filaments, for instance), and then you’d have to find a way to get the wall voltage down (variac/thermistor/etc.), anyway. With my recent Dynakitparts PT (122VAC primary) and a thermistor, I ran my variac up to 130VAC and the voltage on those nodes were still well within the working voltage ratings.

If someone were so inclined, a quick look at available values/sizes suggests that you may be able to select other electrolytics so that there would be a higher working voltage rating for sections two through four of the Triode USA cap board - if really necessary. This would likely mean reduced energy storage but perhaps not so much as to be of great concern.

I noticed that some of the Panasonic electrolytics are being discontinued. This datasheet shows what might be a replacement, but I have noticed a discrepancy in the physical dimensions for the caps used in the second section as listed on the Mouser webpage vs. the datasheet, which I have reported to Mouser. If a suitable replacement is not made, the Triode USA cap board might have to be changed in some way.

BTW, I have been in touch with both Triode USA and Sheldon Stokes, and the cap board Triode now sells for the Stereo 70 is not an SDS Labs design.

I hope I didn't offend anyone. I thought the video was fairly damning evidence of just one aspect of the quad cap design. I remember on the used ST70 I bought a decade ago the quad cap looked like it was welded to the chassis.

For 1950's technology, it was clever and efficient. Today, we can do a lot better.

corndog71 wrote:I hope I didn't offend anyone. I thought the video was fairly damning evidence of just one aspect of the quad cap design. I remember on the used ST70 I bought a decade ago the quad cap looked like it was welded to the chassis.

For 1950's technology, it was clever and efficient. Today, we can do a lot better.

I guess 'better' is somewhat subjective....like sound There are of course a myriad of amps out there using can caps with absolutely no issues what so ever.As I've stated above, my personal preference is to use a cap board, I feel one has more 'control' over the type etc of caps one can use, and to that end, I ended up designing my own which I now use in my versions of the ST120 and M125, and I prefer the 'cleaner' look on top.